"Unchecked runtime.lastError: Could not establish connection. Receiving end does not exist." until pages are reloaded after loading extension

Hi,

Thank you for an excellent starting point for creating an extension.

## Symptom

I noticed that if I start from a browser without my new extension installed and with open pages, load the extension, and then try to use it on these "old" pages, I see this error in the Extensions page:


Which corresponds to this error in the popup's console:

It also happens if I reload the extension when an unpacked extension has been unpacked, and I presume the same thing would happen when the extension gets upgraded after having been installed properly.

## Problem

As pointed out in this [answer](https://stackoverflow.com/a/60323713/345716) the problem is that the "old" pages that were loaded before the extension got installed/reloaded have not been reloaded, so the content script is not present on the pages. This was confirmed by seeing the symptom disappear after I had reloaded the page and then tried using the extension again.

## (Partial?) Fix

I'm guessing a real fix - making the extension work on all pre-existing pages after installation/reloading - isn't possible.

If I make this diff to my vanilla extension:

```diff
diff --git a/src/popup.js b/src/popup.js
index 40f4448..0adb6f5 100644
--- a/src/popup.js
+++ b/src/popup.js
@@ -71,11 +71,12 @@ import './popup.css';
payload: {
count: newCount,
},
- },
- (response) => {
- console.log('Current count value passed to contentScript file');
}
- );
+ ).then((response) => {
+ console.log('Current count value passed to contentScript file', response);
+ }).catch((error) => {
+ console.log('Error passing current count value to contentScript file', error);
+ })
});
});
});
```

Now I see this in the popup's console:

```Error passing current count value to contentScript file Error: Could not establish connection. Receiving end does not exist.'}```

and no error in the extension page. Still not perfect. But a little better.

Better error handling for all three invocations of `sendMessage` methods seems like a good idea in any event (pun intended). See [`chrome.tabs.sendMessage`](https://developer.chrome.com/docs/extensions/reference/tabs/#method-sendMessage) and [`chrome.runtime.sendMessage`](https://developer.chrome.com/docs/extensions/reference/runtime/#method-sendMessage)